1. Field of the Invention
The invention relates to a method of manufacturing luminescent screens for color-picture tubes, wherein a light-sensitive layer is exposed through the shadow mask of the tube.
2. Description of the Prior Art
In German Offenlegungsschrift (DE-OS) No. 24 40 575 stripes of phosphor are produced on a luminescent screen, which stripes vary in width within only narrow limits. A light-sensitive layer of luminescent material on a glass faceplate is exposed through a shadow mask to a light source. A light path is reproduced by a lens so as to correspond to the electron-beam path in the finished tube. On the screen, phosphor stripes of substantially constant width are to be achieved. However, the transmission of the mask varies considerably from the center toward the edge. In addition, the thickness and temperature of the light-sensitive layer of luminescent material applied in the screening process are dependent on screen position. For all these reasons, a filter is used which is located on, directly below, or directly above the lens. The filter influences the intensity of the light beams so that phosphor stripes of only slightly varying width are achieved. As a rule, the filter transmission at the edge is considerably higher than that at the center.
The filter usually consists of a gelatin-soot coating on glass. The production of such a coating is described in detail in DE-OS No. 20 36 684. If a screen is exposed through such a filter, phosphor stripes are obtained whose width stability is fully satisfactory but the edges of the stripes are rather frayed which, during the operation of the tube, gives rise to considerable hue errors in unfavorable cases, as in a uniform white picture.
The use of a rotating diaphragm along with a gelatin-soot filter to obtain position-dependent transmission of light is known (DE-OS No. 20 59 135).